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Carlos III University of Madrid

Advanced Modulation Techniques for Auxiliary Railway Power Supplies

Advanced Modulation Techniques for Auxiliary Railway Power supplies Antonio Lázaro

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Power supply of the train auxiliary services• Air conditioning compressors• Traction motor fans• Lighting• Restaurant wagon services• Buck‐up batteries• Portable devices


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Power supply of the train auxiliary services• Air conditioning compressors• Traction motor fans• Lighting• Restaurant wagon services• Buck‐up batteries• Portable devices

Static converter


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• Air conditioning compressors• Traction motor fans• Lighting• Restaurant wagon services• Portable devices

CC Overhead Power Cable

3

3

33

3

Input filter Inverter AC Filter Transformer

Battery charger

AC loads

• Buck‐up batteries

The static converter

297 kVA / 2400Kg


5

AB

C

Le

Ce

Input Filter

S1 D1

S2 D2S5 D5

S6 D6

Lεcc

Lεcc

Lεcc

Rεcc

Rεcc

Rεcc

Three phase Inverter

Power Transformer and AC Filter

Overhead Power Cable

S2 D2S3 D3

LCC

CCC

LC’

LC’

LC’

RC’

RC’

RC’

CF’ CF’ CF’

RCC

Linea LoadAux. services

Common topology requirements and constraints

High Voltage IGBT• 1700 V• 3300 V• 6500 V

High Input voltage:

• 750 V• 1500 V• 3000 V

Large Input filterSLOW DYNAMIC

LOW SWITCHING FREQUENCY

Input voltage Feed‐forwardOutput voltage feed‐back loop

NO FAST LOOPS CAN BE USEDSCR Battery chargerNON LINEAR BEHAVIOUR

HIGH CURRENT

HARMONICS POLLUTION

AC Output VoltageSTRICT THD SPECIFICATIONS

i3

Control


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Objectives and improvement possibilities

• THD specifications compliance • Cost / weight reduction • Nominal VOUT under minimum VIN & full load

• Topology – Input filter – transformer are imposed

• Inverter modulation can

3Auxiliary services3

3

3AC/DC

VIN

Overhead Power cable

Inverter AC Filter Transformer

Battery charger

Input filter

reduce THD

reduce size – cost – weight of the ac filter

increase the regulation capability


7

2

34

6

7

5

1, 2, 3, 4, 5, 6, 7M11, 2, 3, 4, 5, 6, 7M2

1, 2, 3, 4, 5, 6, 7Mn

M

Look-up Table

1

Control input

Our current experience at GSEPin collaboration with since 2001

• Harmonic Cancellation Technique (HCT)

• Modulation techniques combination

• PWM with Selective Pulse Elimination

• Switching events optimization

Advanced modulation techniques

Core strategy

• Abandon fixed frequency constraints (PWM)

• The best switching events are stored in a Look‐Up Table


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Our current experience at GSEP



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Harmonic Cancellation Technique (HCT)

N3

CF

Rcarga

LF

Lcarga

LFCF CF

Carga CA lineal

Cargador de baterías (No lineal)

i’3

N1

N2

+

VIN

‐

Filtro de entrada

Catenaria

AiA B

iB C iC

Rcarga Lcarga

Rcarga Lcarga

LF

vo+

-

0

i3

3

VAB_1

AC filter Linear loadInverter

+

-

Non-linear Load

vO

+

-

HIGH CURRENT

HARMONICS POLLUTION


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N3

CF

Rcarga

LF

Lcarga

LFCF CF

Carga CA lineal

Cargador de baterías (No lineal)

i’3

N1

N2

+

VIN

‐

Filtro de entrada

Catenaria

AiA B

iB C iC

Rcarga Lcarga

Rcarga Lcarga

LF

vo+

-

0

i3

3

VAB_1

AC filter Linear loadInverter

+

-

Non-linear Load vF

vO

+

-

+ -

HIGH CURRENT

HARMONICS POLLUTION

The voltage drop across the AC filter inductance will distort the output voltage


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The input filter dynamic and the low switching frequency prevent the use of fast control loops, so the inverter modulation is in charge of the THD improvement

Based on conventional SHE (Selective harmonic Elimination) the proposed HCT can generate a new switching pattern:

N

pp

pIN nsenn

V1

)()1(12

4

N

pp

pIN nn

V1

1 )cos()1(112

4

An_vA0An_vA0

Bn_vA0Bn_vA0

• With odd half-wave symmetry• Capable of generating arbitrary harmonics with controlled amplitude and phase

vA0 Eje de simetría de media onda1 2 … … H

t

VIN

0

VIN/2

Origen de ángulos

3 4


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The proposed HCT switching pattern is able to generate arbitrary harmonics with controlled amplitude and phase.

These harmonics will cancel the polluted voltage drop across the AC filter inductance

The Output voltage will be sinusoidal again

+vF-

Cancel each other out

vAB_1

AC FILTERInverter NON Linear Load+ -vF Linear Load

vO

+

‐


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The proposed HCT switching pattern is able to reduce the THD when non‐linear loads are connected to the AC BUS:• NO changes in topology are required• The AC filter size is not increased• Just the control circuit and software have been changed

THD=13% THD=6.5%

SHE HCT

vA

vo

i’3

THD=11.43% THD=4.8 %

VIN=375V

HCTSHE


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Modulation techniques combination

In those cases when the power of the battery charger can be neglected, the modulation gets new goals:

• Reduce THD (switching harmonics)• Reduce size – cost – weight of the ac filter (mainly LAC)• Increase the regulation capability

• The switching harmonic content depends on the modulation index, M

LAC


16

3

SHE worst case

M1.150

THD

• The LAC value is designed to obtain THD<THDmax for the worst harmonic content.

• In the case of the conventional Selective Harmonic Elimination (SHE), this is the minimum M value.

SHE

THDmax

LAC



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3

• In case of conventional PWM with third harmonic injection THIPWM the maximum M presents the higher THD value.

• Space Vector PWM behaves exactly as THIPWM.

LAC


THIPWM worst caseSHE worst case

M1.150

THD

THIPWMSHE

THDmax


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3

• Since the new worst THD is below THDmax, the LAC can be reduced and the THD specification is still complied.

LAC


M1.150

THD

THIPWMSHE

THDmax

New worst THD case

M1.150

THD

THIPWMSHE

THDmax


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• Since the new worst THD is below THDmax, the LAC can be reduced and the THD specification is still complied.


M1.150

THD

THIPWMSHE

THDmax

New worst THD case

M1.150

THD

THIPWMSHE

THDmax

THIPWM or SHE Combined modulator

Size – weight and cost reduction of LAC


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O. Power Cable

3

3 3


M21 n

21 n

i

0.1

0.2

0.80.91

1.15

21 n

21 n21 n21 n

……

…………

MBOUND

Combined modulator

THIP

WM

SHE

M

THIPWM SHE

iA

icarga

vA0

Step change in the Modulation Index around MBOUND


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Patent pending.Application number P201130897

PWM with Selective Pulse EliminationO. Power Cable

3

3 3

M

PWM with Selective pulse elimination

LUT ππ/3 2π/30

27

ππ/3 2π/30

4

2

0

0

5

39

The higher the overmodulation depth, the higher the carrier frequency

HF harmonics are shifted to higher frequencies

0 20 60Harmonic number

0 20 40 60Harmonic number

Har

mon

ic a

mpl

itude

(p.u

.)

0.05

0.1

27 3927


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PWM with Selective Pulse Elimination

0

2

4

6

8

10

12

14

0,7 0,75 0,8 0,85 0,9 0,95 1 1,05 1,1 1,15 1,2 1,25 1,3

Linear Range

Square-wave asymptote

M

THD

(%)

A

B

C

Overmodulation

UC3M patent

Lower THD Lower LAC Better DC BUS exploitation


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• Output Voltage harmonics are function of the switching events, k

• THD will depend on the particular switching pattern (k collection)

• THD can be written as a Objective function to be minimized

• Using a commercial math tool (Matlab or Mathcad, etc.), a mathematical optimization algorithm will provide the optimized switching events

Switching events optimization

π/2 π 3π/2 2π ωt

1

2 3 N‐1N

N

kk

kDCNnO n

nnGTrVV

11_ cos121

·4)(

23

2,...,

2

2

11

221

1··,...,,..h

hTHD

N

kkkN V

VwfVwfMinFO


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Switching events optimization

0

1

2

3

4

5

6

7

8

9

0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 1,00 1,10 1,20 1,30

THD (%)

SHE

THIPWM - SVPWM

OPTIMIZED

4/1.15

Modulation Index, M

M=0.4

M=1.17

• The best results for the whole modulation index range• The Multi-objective functions can be considered


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Current Research LUT-1

LUT-2

LUT-3

MUX

LUT-n

Operating conditions

IGBTs

• Optimized LUTs as a function of the operating conditions

advanced modulation techniques for auxiliary railway … · advanced modulation techniques for...

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